Recent functional magnetic resonance imaging (fMRI) evidence suggests that human visual scene processing is supported by at least two functionally distinct systems: one for visually-guided navigation, including the occipital place area (OPA), and a second for scene categorization (e.g., recognizing a kitchen vs. a beach), including the parahippocampal place area (PPA). However, fMRI data are correlational, and a stronger test of this "two systems for visual scene processing" hypothesis would ask whether it is possible to find cases of neurological insult impairing one ability independent of the other. Toward this end, here we tested visually-guided navigation and categorization abilities in adults with Williams syndrome (WS), a genetic developmental disorder involving cortical thinning in and around the posterior parietal lobe (potentially including OPA, but not PPA). WS adults and mental-age matched (MA) controls (i.e., 7 year old typically-developing children) completed a visually-guided navigation and a categorization task. In the visually-guided navigation task, participants viewed images of scenes, and indicated which of three doors (left, center, or right) they would be able to exit along a complete path on the floor. In the categorization task, participants viewed the exact same scene images, and indicated whether each depicted a bedroom, kitchen, or living room. If visual scene processing is supported by independent visually-guided navigation and categorization systems, then WS adults will be impaired on the visually-guided navigation task, but not on the categorization task. Indeed, we found that WS adults performed significantly worse on the visually-guided navigation task compared to the categorization task, relative to MA controls. These findings provide the first causal evidence for dissociable visually-guided navigation and categorization systems, and further suggest that this distinction may have a genetic basis. Future studies will ask whether patients with PPA damage show the opposite profile from WS, for a full double dissociation.